OpenBSD manual page server

Manual Page Search Parameters

SKEY(1) General Commands Manual SKEY(1)

skey, otp-md5, otp-rmd160, otp-sha1respond to an OTP challenge

skey [-x] [-md5 | -rmd160 | -sha1] [-n count] [-p passphrase] ⟨sequence#⟩ [/] key

S/Key is a procedure for using one-time passwords to authenticate access to computer systems. It uses 64 bits of information transformed by the MD5, RIPEMD-160, or SHA1 algorithms. The user supplies the 64 bits in the form of 6 English words that are generated by a secure computer. This implementation of S/Key is RFC 2289 compliant.

Before using skey, the system needs to be initialized using skeyinit(1); this will establish a secret passphrase. After that, one-time passwords can be generated using skey, which will prompt for the secret passphrase. After a one-time password has been used to log in, it can no longer be used.

When skey is invoked as otp-method, skey will use method as the hash function where method is currently one of md5, rmd160, or sha1.

If you misspell your secret passphrase while running skey, you will get a list of one-time passwords that will not work, and no indication of the problem.

Password sequence numbers count backwards. You can enter the passwords using small letters, even though skey prints them capitalized.

The options are as follows:

| |
Selects the hash algorithm: MD5, RMD-160 (160-bit Ripe Message Digest), or SHA1 (NIST Secure Hash Algorithm Revision 1).
Prints out count one-time passwords. The default is to print one.
Uses passphrase as the secret passphrase. Use of this option is discouraged as your secret passphrase could be visible in a process listing.
Causes output to be in hexadecimal instead of ASCII.

$ skey 99 th91334
Enter secret passphrase: <your secret passphrase is entered here>

login(1), skeyaudit(1), skeyinfo(1), skeyinit(1), skey(5), skeyprune(8)

N. Haller, C. Metz, P. Nesser, and M. Straw, A One-Time Password System, RFC 2289, February 1998.

S/Key is a Trademark of Bellcore.

Phil Karn
Neil M. Haller
John S. Walden
Scott Chasin

March 31, 2022 OpenBSD-7.4